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Discuss What Smart Thermostat for a 2 Wire Connection? Currently Honneywell in the Central Heating Systems area at ElectriciansForums.net


New EF Member
Hi all, new to the forum.
I currently have a Honneywell c901 thermostat set up to control my combi boiler.

I've been looking to buy a smart thermostat to replace the honneywell but when I removed the panel, I see it only has two wires, I hear there are usually 4 wires or more.

Any advice, is it compatible with just two wires?

I've attached some pics.

Kind regards





Forum Mentor
I recommend the nest thermostat. And always recommend that an electrician carries out the installation.

If you go with Nest the thermostat itself can usually use the existing 2 core cable to get the 12V power from the nest heatlink.
The heatlink would be fitted adjacent to the boiler and would connect to the boilers wiring.
The existing thermostat cable will need to be disconnected from the boiler and connect to the 12V terminals of the heatlink.


New EF Member
Thanks for the response, most grateful.

I was wondering if there is some sort of plug and play option because there is a connector I can see from the bottom right of the boiler, see pic attached.

The boiler is a alpha eco 2




Electrician's Arms
Obviously a plumbers wiring.........is that a bit of 2.5 twin and earth in there with the earth cut out lol.

James the Spark1976

electricity is it real or just magic?
Electrician's Arms
Nest is a great bit of kit.
Get a spark to wire it up, it can be expensive if you don’t get it right.
I have had to change boiler control boards where diy guy has wired it wrong and blown the control board.
Not to mention the safety aspect.


New EF Member
I have no idea who did the install whether it was a plumber or a spark as it was installed just before I bought the house. Anyone got a rough idea of price to supply and fit a nest or similar system?


please let me back in to the prison cell.
Electrician's Arms
it would be better to get a spark in a get some qoutes on fitting a nest .
How long is a piece of string .thats a good qestion .

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